# include <stdio.h>
int main()
{
	int i,d,n;
	double b,c,e;
	scanf("%d",&n);
	d=-1 ;
	b=1;   
	for(i=1;i<=n;i++)
    {
       b=b*i/(i*2+1);
	   d=-d;
	   c=d*b;
	   e=e+c;
	}
	printf("%.6f",e);
	return 0;
}
